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Title: Error field impact on mode locking and divertor heat flux in NSTX-U

Abstract

During the 2016 NSTX-U experimental campaign, locked modes in the plasma edge presented clear evidence of the presence of error fields. Extensive metrology and plasma response modeling with IPEC and M3D-C1 have been conducted to understand the various sources of error fields in NSTX-U as built in 2016, and to determine which of these sources have the greatest effect on the plasma. In particular, modeling finds that the error field from misalignment of the toroidal field (TF) coils may have a significant effect on the plasma. The response to the TF error field is shown to depend on the presence of a q = 1 surface, in qualitative agreement with experimental observations. It is found that certain characteristics of the TF error field present new challenges for error field correction. Specifically, the error field spectrum differs significantly from that of coils on the low-field side (such as the NSTX-U error field correction coils), and does not resonate strongly with the dominant kink mode, thus potentially requiring a multi-mode correction. Moreover, to mitigate heat fluxes using poloidal flux expansion, the pitch angle at the divertor plates must be small (~1°). It is shown that uncorrected error fields may result in potentiallymore » significant local perturbation to the pitch angle. Estimates for coil alignment tolerances in NSTX-U are derived based on consideration of both heat flux and core resonant fields independently.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [2];  [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [3]; ORCiD logo [4]
+ Show Author Affiliations
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
  3. General Atomics, San Diego, CA (United States)
  4. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)(SC-24); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1532736
Alternate Identifier(s):
OSTI ID: 1529148
Report Number(s):
SAND-2019-2558J
Journal ID: ISSN 0029-5515
Grant/Contract Number:  
AC02-09CH11466; FC02-04ER54698; SC0012706; AC05-00OR22725; AC04-94AL85000
Resource Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 59; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; tokamaks; error fields; NSTX-U

Citation Formats

Ferraro, N. M., Park, J. -K., Myers, C. E., Brooks, A., Gerhardt, S. P., Menard, J. E., Munaretto, S., and Reinke, M. L. Error field impact on mode locking and divertor heat flux in NSTX-U. United States: N. p., 2019. Web. doi:10.1088/1741-4326/ab22c4.
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Ferraro, N. M., Park, J. -K., Myers, C. E., Brooks, A., Gerhardt, S. P., Menard, J. E., Munaretto, S., & Reinke, M. L. Error field impact on mode locking and divertor heat flux in NSTX-U. United States. https://doi.org/10.1088/1741-4326/ab22c4
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Ferraro, N. M., Park, J. -K., Myers, C. E., Brooks, A., Gerhardt, S. P., Menard, J. E., Munaretto, S., and Reinke, M. L. Wed . "Error field impact on mode locking and divertor heat flux in NSTX-U". United States. https://doi.org/10.1088/1741-4326/ab22c4. https://www.osti.gov/servlets/purl/1532736.
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@article{osti_1532736,
title = {Error field impact on mode locking and divertor heat flux in NSTX-U},
author = {Ferraro, N. M. and Park, J. -K. and Myers, C. E. and Brooks, A. and Gerhardt, S. P. and Menard, J. E. and Munaretto, S. and Reinke, M. L.},
abstractNote = {During the 2016 NSTX-U experimental campaign, locked modes in the plasma edge presented clear evidence of the presence of error fields. Extensive metrology and plasma response modeling with IPEC and M3D-C1 have been conducted to understand the various sources of error fields in NSTX-U as built in 2016, and to determine which of these sources have the greatest effect on the plasma. In particular, modeling finds that the error field from misalignment of the toroidal field (TF) coils may have a significant effect on the plasma. The response to the TF error field is shown to depend on the presence of a q = 1 surface, in qualitative agreement with experimental observations. It is found that certain characteristics of the TF error field present new challenges for error field correction. Specifically, the error field spectrum differs significantly from that of coils on the low-field side (such as the NSTX-U error field correction coils), and does not resonate strongly with the dominant kink mode, thus potentially requiring a multi-mode correction. Moreover, to mitigate heat fluxes using poloidal flux expansion, the pitch angle at the divertor plates must be small (~1°). It is shown that uncorrected error fields may result in potentially significant local perturbation to the pitch angle. Estimates for coil alignment tolerances in NSTX-U are derived based on consideration of both heat flux and core resonant fields independently.},
doi = {10.1088/1741-4326/ab22c4},
journal = {Nuclear Fusion},
number = 8,
volume = 59,
place = {United States},
year = {2019},
month = {6}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1088/1741-4326/ab22c4
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Cited by: 5 works
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Figures / Tables:

Figure 1 Figure 1: Scan of early-time externally applied error field correction (EFC) in 1 MW L-mode discharges in NSTX-U. The applied EFC current waveform is simply a square wave starting shortly after t = 0. The amplitude of the EFC is 600 A (1.2 kA-turns) in all cases, while the phasemore » is varied from shot to shot. In the panel showing core rotation at the bottom right, a phase dependence of the plasma response is clearly visible (see the text for further details).« less
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    Figures / Tables found in this record:

    Figure 1 (p. 3)figure
    Figure 2 (p. 4)figure
    Table 1 (p. 4)table
    Figure 3 (p. 7)figure
    Figure 4 (p. 8)figure
    Table 3 (p. 9)table
    Figure 5 (p. 10)figure
    Figure 6 (p. 11)figure
    Figure 7 (p. 11)figure
    Figure 8 (p. 14)figure
    Figure 9 (p. 15)figure
    Figure 10 (p. 16)figure
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